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Structure physico-chimique des proto-étoiles de faible masse

Abstract : Stars like our sun form by the gravitational collapse of fragments of molecular clouds. During the first stage of its formation (the so called Class 0), the star is deeply embedded in a gas and dust enveloppe, and it is only visible at infrared to millimeter wavelengths. As it evolves, the star progressively disperses this envelope. A protostellar disk remains, which may eventually form planets. In this thesis, I study the physical and chemical structure of low mass protostars. This study is based on ISO observations of water lines, and JCMT and IRAM telescopes observations of formaldehyde lines. In a first part, I study the water lines emission of the protostar NGC1333-IRAS4, which has been observed by ISO-LWS. Using a detailed model of the thermal emission of the protostar, I constrain the density and temperature profile in the envelope, which in turn constrain the central mass and the accretion rate. I also constrain the water abundance inside the envelope, and I show that this abundance is ten times higher in the inner parts of the envelope than in the outer parts. In this inner region, grain mantles evaporate, injecting large amount of water in the gaseous phase. Second, I develop a model of the formaldehyde emission, a molecule which is also abundant in grain mantles, and show that lines of this molecule can also be used to determine the physical and chemical structure of the envelope. Finally, I report a survey of formaldehyde emission of ten low mass Class 0 protostars, obtained at IRAM and JCMT. The comparison between the model predictions and the observations allows me to show that in all the observed protostars but one, formaldehyde is between two and three orders of magnitude more abundant than in the outer envelope. This shows that, like water, formaldehyde is evaporated from grain mantles and that, therefore, all the observed low mass protostars harbor hot cores, where chemistry is very likely influenced, if not dominated, by the evaporation of grain mantles.
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Contributor : Sébastien Maret <>
Submitted on : Friday, January 30, 2004 - 11:50:52 AM
Last modification on : Monday, April 5, 2021 - 2:26:07 PM
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  • HAL Id : tel-00003798, version 3

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Sébastien Maret. Structure physico-chimique des proto-étoiles de faible masse. Astrophysique [astro-ph]. Université Paul Sabatier - Toulouse III, 2003. Français. ⟨tel-00003798v3⟩

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